This invention relates generally to a heat exchanger apparatus for a liquid-cooled internal combustion engine and, more particularly, to a new and improved heat exchanger apparatus which is effective to substantially reduce or eliminate recirculation of air at the fan impeller blade tips and at the fan hub regions so as to substantially improve the air velocity distribution over the air intake face of the heat exchanger or radiator. The present patent application, like patent application Ser. No. 552,090 and patent application Ser. No. 603,490, is related to patent application Ser. Nos. 348,436 and 348,437, both filed on Apr. 5, 1973 and issued, respectively, on Mar. 25, 1975 as U.S. Pat. No. 3,872,916 and on Jan. 7, 1975 as U.S. Pat. No. 3,858,644. Both of the aforementioned patents are assigned to the Assignee of the present patent application.
Most vehicles in general use today are propelled by internal combustion engines and such engines, as is well known, generate heat during the operation of the same. For the most part, the motor vehicle internal combustion engines employed commercially are of the liquid-cool type which entails the circulation, under pressure, of a coolant through the engine for absorbing heat. The correct operating temperature of the engine is maintained by subsequently passing, under pressure, the heated coolant received from the engine through a heat exchanger system or apparatus for dissipating heat from the coolant to the atmosphere and returning the coolant to the engine for recirculation in the engine. Generally, the heat exchange system employed includes a heat exchanger or radiator through which the heated coolant received from the engine is caused to flow. Simultaneously, air is caused to flow through the radiator which absorbs the heat from the heated coolant and carries it out into the atmosphere.
The cooling capacity of a heat exchange system of the type to which the present invention relates is depended upon many factors including the velocity and volume of the air caused to flow through the radiator, as well as the distribution of the air flow over the available heat exchange surface of the radiator. One type of air moving system employed for obtaining the necessary air flow through the radiator in order to maintain the desired operating temperature of the engine involves a fan of the axial flow, suction type. That is, the fan assembly is designed to suck or draw air from the atmosphere and cause the air stream to flow substantially axially through the radiator. Heretofore, in most vehicle installations the air stream, after passing through the radiator, was discharged back over the engine, which is usually spaced axially rearwardly of the fan and radiator.
It has been established that in the majority of conventional motor vehicle heat exchange systems, the axial flow, suction type fans utilized in such systems are extremely inefficient since, under optimum conditions, it is believed only about one-third of the length of each of the radially extending fan impeller blades is actually used for the movement of air axially through the heat exchanger or radiator. In fact, it has been found that the radially outer most one-third of each impeller blade length, the impeller blade tip section, actually pulls in air from an annular area radially rearwardly of the fan impeller blades and the fan shroud rather than forwardly thereof. Thus, the tip end of each fan blade is being used to merely recirculate air rather than to pull cooling air axially through the heat exchange core air passages. In a similar manner, the radial innermost one-third of each fan impeller blade at the hub region of the fan pulls in air from the area axially spaced rearwardly of the fan (instead of forwardly thereof) and thereafter discharges such air rearwardly of the fan. Consequently, as a result of such air recirculation phenomenon, only about the middle one-third of each fan impeller blade is actually effective in moving a cooling stream of air axially through the radiator. Approximately two-thirds of the energy necessary to drive the fan is thus wasted in the recirculation of air at the tip and hub regions of the fan.